A valve element opening/closing device has been conventionally known in which a valve element is driven by a motor as a drive source to open and close a flow path for refrigerant of a refrigerator or the like. For example, in Japanese Patent Laid-Open No. 2003-148645 (first patent reference), a valve element opening/closing mechanism of a so-called linearly moving drive type valve element is described in which a needle valve is attached to a screw member, and the screw member is rotated by a motor to advance and retreat in an axial direction. Thus, an opening from which refrigerant flows out is opened or closed.
Further, in Japanese Patent Laid-Open No. 2004-293573 (second patent reference), an opening/closing mechanism of a valve element is described in which a disk valve provided with an opening part is rotated by a motor, and when the opening part of the disk valve is coincided with one of outflow ports provided in a valve seat plate, the corresponding outflow port is in an opened state.
However, in the above-mentioned first patent reference, the moving amount of the screw member in the axial direction with respect to rotation amount of the motor is required to be controlled accurately. Therefore, a male screw part and a female screw part with a high degree of accuracy are required in the screw member and a cylindrical part with which the screw member is threadedly engaged. Therefore, mass-productivity is low. In addition, since a moving amount in the axial direction of the screw member per rotation of the motor is small, the number of motor rotations required to move the needle valve to open/close increases. Thus, energy efficiency is low and response of an opening/closing operation of the valve element is slow.
Further, in the above-mentioned second patent reference, the disk valve is disposed to face-contact with the valve seat plate which is provided with the outflow port, which is different from the case where the valve element linearly moves to open and close the outflow port for refrigerant as described in the first patent reference. However, in this case, the starting performance of the valve element opening/closing device is lowered by a frictional force due to sliding of the disk valve on the valve seat plate.
Further, the valve seat which is used in the above-mentioned valve element opening/closing devices is often fixed to a plate in the valve element opening/closing device by brazing. Therefore, brazing material flowing into a space between the valve seat and the plate may flow out to an abutting face of the valve seat with the valve element to cause roughness of the abutting face to increase. Accordingly, the sealing property at the time of abutting of the valve element with the valve seat, which is secured by polishing or the like, is deteriorated and the abutting face of the valve element with the valve seat may be damaged by an edge of the brazing material adhered to the abutting face of the valve seat.